Add a test for the noop backend.

tests/Cargo.toml

@@ -22,11 +22,16 @@ name = "wgpu-compile-test"
 path = "compile_tests/root.rs"
 harness = true
 
+[[test]]
+name = "wgpu-validation-test"
+path = "validation_tests/root.rs"
+harness = true
+
 [features]
 webgl = ["wgpu/webgl"]
 
 [dependencies]
-wgpu.workspace = true
+wgpu = { workspace = true, features = ["noop"] }
 wgpu-macros.workspace = true
 
 anyhow.workspace = true

tests/validation_tests/noop.rs

@@ -0,0 +1,61 @@
+//! Tests of [`wgpu::Backend::Noop`].
+
+use std::sync::atomic::{AtomicBool, Ordering::Relaxed};
+use std::sync::Arc;
+
+#[test]
+fn device_is_not_available_by_default() {
+    let instance = wgpu::Instance::new(&wgpu::InstanceDescriptor {
+        backends: wgpu::Backends::NOOP,
+        ..Default::default()
+    });
+
+    assert_eq!(
+        pollster::block_on(instance.request_adapter(&wgpu::RequestAdapterOptions::default())),
+        None,
+        "noop backend adapter present when it should not be"
+    );
+}
+
+#[test]
+fn device_and_buffers() {
+    let instance = wgpu::Instance::new(&wgpu::InstanceDescriptor {
+        backends: wgpu::Backends::NOOP,
+        backend_options: wgpu::BackendOptions {
+            noop: wgpu::NoopBackendOptions { enable: true },
+            ..Default::default()
+        },
+        ..Default::default()
+    });
+    let adapter =
+        pollster::block_on(instance.request_adapter(&wgpu::RequestAdapterOptions::default()))
+            .expect("adapter");
+    let (device, queue) =
+        pollster::block_on(adapter.request_device(&wgpu::DeviceDescriptor::default(), None))
+            .expect("device");
+
+    assert_eq!(adapter.get_info().backend, wgpu::Backend::Noop);
+
+    // Demonstrate that creating and *writing* to a buffer succeeds.
+    // This also involves creation of a staging buffer.
+    let buffer = device.create_buffer(&wgpu::BufferDescriptor {
+        label: Some("hello world"),
+        size: 8,
+        usage: wgpu::BufferUsages::COPY_DST | wgpu::BufferUsages::COPY_SRC,
+        mapped_at_creation: false,
+    });
+    assert_eq!(buffer.size(), 8);
+    queue.write_buffer(&buffer, 0, &[1, 2, 3, 4]);
+    queue.write_buffer(&buffer, 4, &[5, 6, 7, 8]);
+
+    // Demonstrate that we can read back data from the buffer.
+    // This also involves copy_buffer_to_buffer().
+    let done: Arc<AtomicBool> = Arc::default();
+    let done2 = done.clone();
+    wgpu::util::DownloadBuffer::read_buffer(&device, &queue, &buffer.slice(..), move |result| {
+        assert_eq!(*result.unwrap(), [1, 2, 3, 4, 5, 6, 7, 8],);
+        done.store(true, Relaxed);
+    });
+    device.poll(wgpu::Maintain::Wait);
+    assert!(done2.load(Relaxed));
+}

tests/validation_tests/root.rs

@@ -0,0 +1,3 @@
+//! Tests of the [`wgpu`] library API that are not run against a particular GPU.
+
+mod noop;